Method for improving the corrosion resistance of a metal surface



United States Patent METHGD FGR WRUVENG THE QQRRGSEUN RESISTANCE @F A METAL EURFAtCE Robert C. Hediund, Midland, Mich, assigner to Dow Corning (Iorporation, Midland, Mich, a corporation of Michigan No Drawing. Continuation oi application Scr. No. 808,573, Apr. 24, 1959. This application Aug. 23, 1962, her. No. 218,816

14 rClaims. (Cl. 117-75) The present invention relates to processes for protecting metal surfaces against corrosion, to articles comprising metal surfaces which have been so protected, and to particular polishing compositions capable of so protecting metal surfaces. The present application is a continuation of application Serial No. 808,573, filed April 24,

1959, and now abandoned.

The corrosion of metals, both from natural and manmade causes, is an age old problem. This corrosion ranges from the various degrees of rusting which can spoil both the appearance and effectiveness of metals such as iron and steel, to the relatively slight degree of oxidation which in general affects only the appearance of metals such as copper and aluminum. It is an object of the present invention to provide an improved means for preventing or retarding such corrosion in metals, and particularly to provide anti-corrosion protection of a sort which does not alter the appearance of the metal itself.

The process of this invention comprises wetting the metal surface with an aminated organosilicon compound selected from the group consisting of (1) polyaminoalkylsilanes of the formula (RO) Si(R'Z where each R is an alkyl radical of less than 4 carbon atoms, R is an allphatic hydrocarbon radical containing a number of carbon atoms selected from the group consisting of l and more than 2 carbon atoms and having a valence of n+1 where n is an integer of at least 1, and Z is a monovalent radical attached to R by a carbon-nitrogen bond and is composed of carbon, nitrogen, and hydrogen atoms and contains at least 2 amine groups, the ratio of carbon atoms to nitrogen atoms in the substituent (R"',, being less than 6:1, (2) alcohol-soluble hydrolyzates of (1), and (3) acid salts of (l) and (2), and drying said metal surface.

The aminated organosilicon compounds employed here in are fully described in US. Patent No. 2,971,864 and copending application Serial No. 75 3,ll5, filed August 4, 1958 (now abandoned), both of which are assigned to the assignee of the present invention and which are incorporated herein by reference.

In the compounds of the formula (RO) Si(R'Zn), R can be any alkyl radical of less than 4 carbon atoms, i.e. methyl, ethyl, propyl and isopropyl radicals. R can e any aliphatic hydrocarbon radical containing 1 or more than 2 carbon atoms and having a valence of at least two,

i.e. it can include in any aliphatic configuration any combination and any number of methyl, vinyl, methylene, vinylene,

and

groups within the scope of the claims. The R radicals can be the same or different.

Z can be any monovalent radical attached to R through a carbon-nitrogen linkage, which is composed of hydrogen, carbon and nitrogen atoms, in which all of the nitrogen atoms are present as amine groups, and in which 3,l'i5,92l Patented Mar. 3% 1965 there are at least two amine groups per Z radical. The term amine groups comprises primary amine, secondary amine (including imine) and tertiary amine groups.

The hydrolyzates of the defined polyaminoalkylsilanes which can be employed herein include the so-called partial hydrolyzates as well as the completely hydrolyzed material. The hydrolyzates should be in a form which is still soluble in some inert solvent, however, and solubility in an alcohol seems to be the best criterion for defining operative hydrolyzates. if one of the defined hydrolyzates is soluble in any alcohol whatsoever it is suitable for use herein, for such solubility permits the use of a liquid form of the hydrolyzate even if the hydrolyzate itself is a solid. Solubility in an alcohol also is indicative of the fact that the completely condensed form of the hydrolyzate (i.e., the form in which substantially all of the polymeric units have become (Z RUSiO units) has not yet been reached. it is preferred that such complete condensation is not achieved, it achieved at all, until after the metal has been wetted.

The hydrolyzates are described in detail in the aforesaid copending application Serial No. 753,115. in brief, the hydrolyzates can be formed by mixing one or more of the defined monomeric polyaminoalkylsilanes with water in any proportion. This brings about the hydrolysis of some or all of the (-OR) radicals to form siliconbonded OH groups, some of which can then condense to form SiGSi linkages. Hydrolyzates are also formed, of course, when the defined silanes are exposed to atmospheric moisture.

l t is thought that those hydrolyzates which are still soluble in an alcohol will have an average of at least about 0.5 of the silicon-bonded OH and/or (OR) groups per silicon atom. Thus the silanes and hydrolyzates employed herein may both be defined as encompassed Within the general formula where R, R, Z, and n are as previously defined, x has a value of from 0 to 3 inclusive, 2 has a value of from 0 to Z inclusive, and the sum of x-l-y has a value of from 0.5 to 3 inclusive. it is felt, however, that the lack of more detailed knowledge as to the distribution of the various types of units within this formula when it represents a polymer renders such a definition less satisfactory than that which defines the hydrolyzed material as an alcoholsoluble hydrolyzate.

The defined aminated orgariosilicon compounds can be applied to the metal surface to be treated in any convenient manner, for example by dipping, spraying, or brushing, so long as the surface is thoroughly wetted therewith. Most of the defined compounds are liquid, and metal surfaces can be treated with such compounds per se. Those of the compounds which are not liquid are preferably employed in the form of a solution in an inert solvent, although it is to be understood that semisolid forms or" the compounds can be applied as such by rubbing them onto the metal, as in a polishing or buffing type of application. Thus the term wetting is used herein as inclusive of coating with a non-liquid mawater miscible alcohol into the aqueous solution. the aminated compounds are in general even more soluble insoluble in water.

compounds are employed. Thus for both economy and erllciency it is preferred that the defined compounds be applied in the form of a solution in an inert solvent. Concentrations of from about 0.125 to about 26% by weight of the defined compounds in the solution have been found to be highly suitable, with the most preferred range being from about 1 to 5% by weight.

Most of the defined silanes, hydrolyzates, and salts are soluble in water, and thus water is the least expensive of the inert solvents contemplated here. Often, however, an aqueous solution does not Wet the surface of the metal as thoroughly as desired. In such a case, the wetting properties can be improved by incorporating a Since in alcohols than in water, the amount of alcohol employed can range up to and including 109% of the total solvent present. in general, the best alcoholi solvents for the defined compounds are those which are miscible with water, as for example the lower aliphatic alcohols, e.g., methanol, ethanol, propane and isopropauol, and various glycols and others thereof, e.g., ethylene glycol and its monoinethyl, monoethyl, and monobutyl ethers, and propylene glycol and its comparable others.

The monomeric silanes which can be used in. accordance with this invention are soluble not only in water and alcohols, but also in hydrocarbon solvents such as benzene, toluene, xylene, and the aliphatic petroleum hydrocarbon solvents. The hydrolyzates are much less soluble'in such hydrocarbon solvents, however. Since the monomeric silanes are hydrolyzed when exposed to at mospheric moisture, solutions of such silanes in hydrocarbons may tend to became hazy or even may develop an immiscible phase when they are stored for long periods in containers which are not air-tight, or when they are repeatedly exposed to the atmosphere. For this reason it is preferred that when a hydrocarbon solvent is used, at least a small amount of an alcoholic type of solvent be mixed therewith. Preferably any such mixture should contain at least 5% of the alcholic solvent based on the weight of the mixed solvents.

Hydrocarbon others also are suitable solvents for both the monomers and hydrolyzates employed herein. The others can be either straight chain, as in lower alkyl others, or cyclic, as in dioxane.

After the metal surrace is wetted by one or more of the defined arninated compounds, anti-corrosion properties are developed by merely allowing the surface to dry. This can be done under atmospheric conditions, but to expedite the process it is often desirable to employ an elevated temperature. In the usual case, the surface will be dried until there is no film remaining which is visible to the naked eye. Of course if a relatively thick, tangible film has been deposited by the use of a high concentration of the aminated compound, a correspondingly visible, tangible dried film will remain. Grdinarily, however, it is preferred to operate in such a manner that no visible film remains after any solvent present has been allowed to evaporate.

The film of aminated organosilicon compound which remains after merely drying the treated metal surface imparts corrosion resistance to the metal, but is rather low in abrasion resistance and is likely to be rather water soluble until it has been exposed to ordinary temperatures for a long time. Such properties are usually objectionable, for under many conditions of use the protective action or" the aminated compounds would be removed by wearing or washing. For this reason it is preferred that after Wetting the metal surface, the resulting visible or invisible film be cured until it is suostantially Substantially insoluble is used her to mean that a stream of running water does not remove the film rrom the treated surface, as evidenced by the retention of anti-corrosion properties by that surface.

Curing to the desired substantially water insoluble state Ail can be achieved by heating the treated metal surface. In general, the higher the temperature of cure, the less is the time required to arrive at a sufficiently cured state. Preferably the cure is carried out at a temperature of at least C., and optimum results are obtained at temperatures of at least to C. At 150 C. a sufficient cure can be obtained in as little as 15 minutes, but a time of at least 4-5 minutes to 1 hour at that temperature is generally better. Any additional time at about 150 C. seems to have no effect whatsoever, and is neither beneficial nor detrimental. It will be obvious that the nature of some treated metal articles is such that the desired curing can take place during the initial use of the article, and a separate, specific curing step will be of no particular benefit. Temperatures in the region of 225 to 250 C. tend to lessen the effectiveness of the treatment, and prolonged exposure at such temperatures is preferably avoided.

C-uring catalysts can of cour e be employed to lessen the time and/ or temperature required to obtain optimum curing. These catalysts can be the known organosiloxanc curing catalysts, such as the metal salts of carboxylic acids, or they can be materials which are reactive toward the amine functional groups to provide cross-linked poly mers.

It is not known What form is talren by the dried or cured film of aminated organosilicon compound on the treated metal surface, and thus such a film is best defined by reference to its original composition prior to drying and/ or curing.

Any metal can be treated in accordance with this invention, but the greatest benefits can be observed with regard to copper, iron, aluminum, tin, magnesium, and alloys of any of these, particularly steel. The treatment affords protection against both rusting and dicoloration, and thus is applicable to such diverse articles as steam pipes and boilers on the one hand and copper ornamentation and cooking utensils on the other. Rusting or discoloration problems exist in. a multitude of metal articles where the metal is present in innumerable forms of rods, wires, sheets, blocks, etc, and the invention encompasses the treatment of any of such forms. When the treatment is made from a more or less dilute solution of the defined compounds, protection against corrosion can be obtained with no visible change in the original appearance of the metal.

The defined aminated compounds can be incorporated into conventional metal cleaning and polishing compositions if desired, to provide a means of cleaning the metal and laying down a protective film at the same time. Such compositions can be based on an aqueous system, taking the form of suspensions or emulsions, or based on an organic solvent system, taking the form of suspensions, solutions, or pastes. Either system can contain the conventional optional additives such as abrasive (e.g., finely divided silica), waxes (particularly the neutral or non-acid waxes such as the parafiin or mineral waxes, ozokerite, and montan waxes) and emulsifying agents. The aqueous systems can contain thickeners such as methylcellulose or carboxy methylceilulose, the solvent systems can be thickened by the well known metal salt thickeners such as aluminum stearate. Additional polishing agents such as the dialkylsiloxane fiuids or alkylarylsiloxane fluids can also be incorporated into the polishing compositions if desired.

Preferred organic solvents for the compositions include mineral spirits and hydrocarbon solvents such as toluene and xylene. Preferably the polishing compositions contain from about 1% to about 10% by weight of one or more of the defined aminated compounds. The other constituents can be present in practically any conceivable proportions, or can be totally absent, depending upon what form is' desired for the composition. The amount of water or organic solvent present will ordinarily range from about to about 98% based on the weight of the entire polishing composition, and either will perform suitably as a liquid carrier or extender for the aminated compounds.

The following examples are illustrative only and are not intended to limit the invention, the scope of which is properly delineated in the claims. All parts and percentages are by weight unless otherwise indicated. The symbols Me and Ph have been used to represented methyl and phenyl radicals respectively.

Example 1 The aminated compounds for use in this example were prepared as follows: HSiCl and allyl chloride were reacted at reflux temperature in the presence of H PtCl as a catalyst to produce ClCH CH CH SiCl The latter was recated at room temperature with methanol in a molar ratio of 1:3 to produce ClCI-I CH CI-I Si(OCH This was added slowly to a refluxing stream of ethylene diamine through the top of a distillation column in a ratio of about 2.5 mols of the diamine per gram atom of chlorine. The reaction was instantaneous, and the cooled reaction product separated into two layers. The lower layer, consisting of a solution of in the excess ethylene diamine, was discarded. The small amounts of methanol and ethylene diamine which were present in the top layer were removed therefrom by a strip distillation, leaving a residue of what will hereafter be referred to as the crude aminated product A portion of the later crude product was fractionated and it was found that it contained about 70 to 80 percent of the pure product. The remainder comprised the corresponding siloxanes and siloxanols which had developed by the partial hydrolysis which occurred throughout the handling of the reactants, along with small portions of high boiling products in which more than one hydrogen atom of the starting ethylene diamine had reacted with the chloropropyl substituted silane. The pure product boiled at 140.5 C. at mm. Hg, 11 1.4416, d l 1.01.

A stock solvent solution was prepared by mixing 70 parts xylene with 25 parts of the monomethyl ether of propylene glycol (the latter being known and available in the trade as Dowanol 33B). Using this mixture as the solvent, solutions were prepared containing 0.125%, 0.5%, 1%, 2%, 5%, 10%, and 20% respectively of the crude aminated product from above. The eifectiveness of each concentration was tested by dipping strips of copper foil therein, allowing the strips to dry at room temperature for about 5 minutes, and then heating the treated strips for either 15 minutes, or 1 hour at 150 C. The strips were tested by heating them at 200 C. in a circulating air oven. Under these conditions, control strips which had not been treated were found to become oxidized and discolored in 15 minutes, whereas none of the treated strips showed signs of discoloration. After one hour at 200 C. it was found that those strips treated with solutions containing from 0.125 to 1% of the aminated compound showed gradually decreasing degrees of discoloration as the concentration of the treating solutions increased. Those strips treated with solutions of 2 or 5% concentration showed no discoloration or oxidation. At concentrations of 10% or more there was no oxidation of the copper itself but there was some slight discoloration of the more tangible film which had been deposited from these higher concentrations.

Some of the tested strips were washed with water and retested. It was found that in the case of those which had been cured for one hour the protective action was retained, whereas those which had been cured for only 15 minutes showed some loss of protective action. This illustrated the fact that the greater length of cure had rendered the protective film less soluble in water.

When the above treatment of copper strips was repeated using the pure product rather than the crude, it was found that practically identical results were obtained. The same results were also obtained when either the pure or crude products were applied from aqueous solutions, except that spotty areas existed where the protection against discoloration was less, thus indicating that aqueous solutions provided less complete wetting of the metal. When ethoxyor isopropoxy-sulbstituted silanes are employed in place of the above described methoxy silanes, equivalent results are obtained.

Example 2 After thorough cleaning and polishing, portions of the copper bottoms of a copper clad frying pan and a copper clad sauce pan were brushed with a solution containing 5% of the crude aminated product from Example 1 dissolved in the xylene-Dowanol mixture of that example. The pans were allowed to air dry and were cured for one hour at 150 C. The resulting protective films were invisible, and the pans had the appearance of untreated but polished copper clad pans. The pans were placed in normal household use for a period of three months. At the end of this time the treated portion of the frying pan showed no discoloration whatsoever except in small areas where there had been obvious abrasion against the heating coil of the stove, whereas the untreated portion of the frying pan had taken on the typical tarnished appearance of used copper. The sauce pan was similarly discolored in its untreated portion, but showed no discoloration in the treated area, said area remaining as bright as freshly polished copper.

Example 3 Three different portions of the pure aminated product from Example 1 were mixed respectively with an amount of water calculated to hydrolyze 50%, and of the silicon-bonded methoxy groups. Each hydrolyzate was then dissolved in the methyl ether of propylene glycol in proportions such as to provide 5% of each hydrolyzate respectively. Copper strips were dipped in these solutions, then cured and tested as in Example 1. No particular differences from the results of Example 1 could be observed.

Example 4 When one of the following halohydrocarbons is employed in the reactions illustrated in Example 1 in place of the allyl chloride, the indicated polyarninoalkylalkoxysilanes are produced.

CH2=CHCHBrCHzBr CHz C (CHaCDz 7 When HSiCl is reacted with allyl chloride and the product methoxylated as described in Example 1, then the methoxylated product reacted with one of the following polyamines, the indicated silanes are produced:

5239 is an alkyl radical of less than 4 carbon atoms, and drying said metal surface.

2. A method for improving the corrosion resistance of ametal surface subject to corrosion which comprises Polyamine Silane H NCH2CH NI-ICH CH1NH H H2N(CHz)uNH2 and MeHN(OHz)sNHMe HzNCHz-GHMtENHz and (MeO)aSiCHzCHzCHzNHCHMeCHzNHn CHzCH2NHz (MeOhSiCHzCHzOHzNHCHzOHzCH(CH2)sNH Likewise when N,N-dimethyl-p-phenylenediamine is reacted with (MeO) SiCI-I Cl, the product Example 5 Solutions were prepared containing 2%, 5%, and respectively of the crude aminated product of Example 1 dissolved in the xylene-Dowanol mixture of that example. Steel test panels were dipped in one of these solutions, air dried, and cured for 1 hour at 150 C. Each panel was then dipped in a catalyzed xylene solution containing of an organosiloxane resin, which resin consisted of a mixture of 75 parts of a copolymer (A) containing 28 mol percent MeSiO units, 27 mol percent PhSiO units, 40 mol percent PhMeSiO units, and 5 mol percent Ph SiO units, said copolymer containing 1% siliconbonded hydroxyl groups, and parts of a copolymer (B) of identical unit composition but containing 3.5% silicon-bonded hydroxyl groups. The catalyst in this resin solution was benzyltrimethyl ammonium acetate, present in an amount of about 0.2% based on the weight of the organosiloxane resin present in the solution. Such a resin system is described in detail in US. Patent No. 2,906,734. The resin deposited in this second dipping was cured for 1 hour at 150 C. The test panels were then subjected for 120 hours to a spray of an aqueous solution held at 95 P. which contained 20% NaCl. The panels showed only traces of rusting after this severe test.

As a comparison, identical steel panels were dipped only in the above described xylene solution of the organosiloxane resin and cured as above, i.e., no preliminary treatment with the crude aminated product was given. These test panels were subjected to the same salt spray conditions described above, and each exhibited severe rusting from the test.

That which is claimed is:

1. A process for protecting a metal surface against corr-osion which comprises wetting the metal surface with an aminated organosilicon compound selected from the group consisting of compounds of the formula (R0) Si[ (CH NHCH CH NH and alcohol-soluble hydrolyzates thereof, Where each R Wetting the metal surface with an aminated organosilicon compound selected from the group consisting of compounds of the formula and alcohol-soluble hydrolyzates thereof, where each R is an alkyl radical of less than 4 carbon atoms, and allowing the wetted surface to dry until no visible aminated organosilicon compound remains.

3. A method for improving the corrosion resistance of a steel surface, which comprises wetting said surface with a compound of the formula a s 2 B 2C 2 2] and drying said surface until no visible liquid remains.

4. A process for protecting a metal surface against corrosion which comprises Wetting the metal surface with an aminated organosilicon compound selected from the group consisting of compounds of the formula and alcohol-soluble hydrolyzates thereof, Where each R is an alkyl radical of less than 4 carbon atoms, and ouring the resulting film on said surface untilthe film is sub stantially water insoluble.

5. A process in accordance with claim 4 wherein the film of aminated organosilicon compound is cured at a temperature of at least C.

6. A process for protecting a metal surface against corrosion which comprises wetting said surface with a solution consisting essentially of from 0.125 to 20% by Weight of an aminated organosilicon compound dissolved in an inert organic solvent, said aminated organosilicon compound being selected from the group consisting of compounds of the formula and alcohol-soluble hydrolyzates thereof, where each R is an alkyl radical of less than 4 carbon atoms, and drying said surface until no visible liquid remains.

7. A method for improving the corrosion resistance of a steel surface which comprises wetting said surface with a solution consisting essentially of from 1 to 5% by weight of an aminated organosilicon compound of the formula (CH O) Si[(CH NHCH CH NH dissolved in an alcoholic solvent for said compound, and curing the resulting film of the aminated organosilicon compound at a temperature of at least C. until no visible liquid remains and until said film has been rendered substantially insoluble in water.

8. A process which comprises applying a prime coating to metal by wetting the metal surface with an aminated organosilicon compound selected from the group consisting of compounds of the formula and alcohol-soluble hydrolyzates thereof, where each R is an alkyl radical of less than 4 carbon atoms, drying said metal surface, and applying a coating of a polymeric organosiloxane resin over said prime coating.

9. A process in accordance with claim 8 wherein the aminated organosilicon compound is a compound of the formula 10. A process which comprises applying a prime coating to metal by wetting the metal surface with an aminated organosilicon compound selected from the group consisting of compounds of the formula and alcohol-soluble hydrolyzates thereof, where each R is an alkyl radical of less than 4 carbon atoms, curing the resulting film on said surface until the film is substantially water-insoluble, and applying a coating of a polymeric organosiloxane resin over said prime coating.

11. A process in accordance with claim 10 wherein the film of aminated organosilicon compound is cured at a temperature of at least 100 C.

12. A process which comprises applying a prime coating to metal by wetting the metal surface with an aminated organosilicon compound selected from the group consisting of compounds of the formula (R) Si[ CH NHCH CH NH and alcohol-soluble hydrolyzates thereof, where each R is an alkyl radical of less than 4 carbon atoms, drying said metal surface, and applying a coating of a polymeric organosiloxane resin over said prime coating, the said resin being one in which organic radicals are attached to silicon by carbon-silicon linkages and said radicals consist essentially of radicals selected from the group consisting of methyl and phenyl radicals.

13. A method for improving the corrosion resistance of a copper surface, which comprises wetting said surface With a compound of the formula References Cited by the Examiner UNITED STATES PATENTS 8/57 Brown 260-28 RICHARD D. NEVIUS, Primary Examiner. 

8. A PROCESS WHICH COMPRISES APPLYING A PRIME COATING TO METAL BY WETTING THE METAL SURFACE WITH AN AMINATED ORGANOSILICON COMPOUND SELECTED FROM THE GROUP CONSISTING OF COMPOUNDS OF THE FORMULA 